I’d be more concerned about it not grouping than not being zeroed.
I’d suspect either he didn’t remount the scope correctly, and it was slightly loose, or worst-case, did some damage to the crown.
Check that the mounts and rings are properly secured and try to dial it in again.
I’ve had better luck bore sighting my inlines by pulling the breach plug and placing the gun in a steady rest, sighting down the bore and adjusting the scope than I have with laser bore sights. I think there’s just too much “wiggle room” in a 50 cal bore for all but the highest-end lasers.